MTA code: mail.TRY_AGAIN

HELP I installed zimbra 8.0.7_GA_6021 NETWORK after installation and testing of zimbra, I created two accounts but when I go to send messages between accounts created me it has an error "There was an unknown error occurred (mail.TRY_AGAIN).
method: [unknown]
msg: try again: Unable to connect to the MTA
code: mail.TRY_AGAIN
detail: soap: Receiver
trace: qtp196183286-476:https://192.168.0.110:443/service/so...b70109aa529e4e
request: "